1. Field of the Invention
The present invention relates generally to mobile communication systems, and more specifically to a technique for multicast sessions between home domain and visiting mobile nodes.
2. Description of the Related Art
Mobile IP protocol developed by the Internet Engineering Task Force guarantees reachability for unicast packets, (http://www.ietf.org/rfc/rfc 2002.txt.). According the mobile IP protocol, a mobile node belongs to a link (or home link of the mobile node) of a management domain (or home domain of the mobile node) and on this home link the mobile node is assigned an address. A mobility management agent is set up on the home link as a home agent of the mobile node. In order to guarantee reachability of unicast packets for a mobile node visiting another link of the home domain or a link of a foreign management domain, the mobile node acquires a temporary address, known as a care-of address, from the visited link and communicates this care-of address to the home agent. If the home agent receives a packet destined for the mobile node, it formulates a packet with the care-of address and encapsulates the received packet in the formulated packet and transmits it to the mobile node, now visiting the foreign domain.
Hierarchical mobility management protocol is known. This protocol can be used in combination with the mobile IP protocol. See “Hierarchical MIPv6 mobility management”, (http://www.ietf.org/internet-drafts/draft-ie-tf-mobileip-hmipv6-03). According to the hierarchical mobility management scheme, mobility management agents (or mobility agents) are provided in a foreign domain. A mobile node, when visiting the foreign domain, notifies its home agent of the address of a mobility agent as a care-of address of the mobile node and notifies the mobility agent of its own home address and a care-of address obtained from a link to which the mobile node is currently attached. The home agent, on receiving a packet destined to the mobile node, formulates a packet destined to the mobile-notified care-of address (i.e., the address of the mobility agent). The received packet is encapsulated in the formulated packet and transmitted. In response to this packet, the mobility agent decapsulates it to extract the inner packet, examines its destination address, formulates a packet destined to a care-of address corresponding to the home address that matches the destination address and encapsulates the extracted packet in the formulated packet for transmission.
Mobile nodes, when visiting a foreign domain, are able to participate in a multicast session with their home mobile nodes by using a multicast (MC) address which is locally unique to the home domain. In this multicast session, the mobile IP protocol requires that visiting mobile nodes notify the home domain of their care-of addresses assigned to them from the visiting domains. In the home domain, a multicast packet is encapsulated in packets respectively destined to the care-of addresses and individually tunneled to the visiting domains. Each visiting mobile node decapsulates the packet to extract the inner multicast packet.
As a result, in the prior art techniques, the network bandwidth resource is consumed in proportion to the number of mobile nodes visiting foreign domains. Furthermore, with the prior art hierarchical mobility management scheme, an increased burden is placed on mobility management nodes (such as home agents and mobility agents) since the mobility agent of a foreign domain must perform as many encapsulation processes as there are mobile nodes visiting the foreign domain.